Rotary actuator and bearing support therefor

ABSTRACT

An axial force exerting in the axial direction of a rotary actuator is uniformly applied to a plurality of axially arranged ball bearings of a bearing set to hold inner and outer rings of each ball bearing in optimum position, thereby heightening the rigidity of the bearing set. A waved washer is interposed between the ball bearings and distributes the axial force so as to axially slide the ball bearings. While being slidden to the optimum positions, the ball bearings are bonded for fixing.

This is a continuation of application Ser. No. 943,750, filed Dec. 19,1986 now U.S. Pat. No. 4,892,423.

BACKGROUND OF THE INVENTION

This invention relates to a rotary actuator using ball bearings and moreparticularly to this type of rotary actuator suitable for use in arotary disc storage device.

JP-A-No. 60-102862 published on June 7, 1985 discloses a rotary actuatorcomprising bearing sets each having a plurality of ball bearings. Theshaft structure of the rotary actuator can be simplified andmanufactured at low costs by using the rotary actuator the rotationalshaft of which is supported at its upper and lower ends by a ballbearing as in the above publication. But the rigidity of the single ballbearing at the both ends is small in the radial direction, resulting ina low mechanical resonance frequency of a rotary part of the rotaryactuator. Consequently, vibrations are liable to be induced in the servocontrol process to degrade accuracy of positioning of a magnetic head ona magnetic disc. In another rotary actuator, its rotational shaft issupported at upper and lower ends by needle bearings for the purpose ofimproving radial rigidity. Since the radial rigidity of the needlebearing is large, a rotary part of the rotary actuator can have a highmechanical resonance frequency and is not liable to induce vibrations inthe servo control. Disadvantageously, however, this rotational shaft hasa complicated shape and requires additional thrust bearings, thusleading to expensiveness.

SUMMARY OF THE INVENTION

An object of this invention is to provide a mechanical arrangementwherein inner and outer rings of each ball bearing of a bearing set arein uniform contact with all of the balls arranged side by sidethroughout the circumference of the rings to increase rigidity of thebearing set even when ball bearings of the standard specification areused for the bearing set, thereby making it possible to rigidly supportthe rotational shaft of the rotary actuator.

Another object of this invention is to make a rotary part of the rotaryactuator having a high resonance frequency which is not liable to inducevibrations in the servo control and thus to provide an inexpensivemagnetic disc device capable of accurate positioning of the magnetichead.

Still another object of this invention is to provide a mechanicalstructure which can effectively heighten the radial rigidity, withoutresort to the additional provision of needle bearings and thrustbearings, by using inexpensive ball bearings of the standardspecification which are commensurate with a simplified shape ofrotational shaft.

Yet still another object of this invention is to provide a mechanicalstructure which can realize a high-rigidity ball bearing set byuniformly distributing a load applied on the shaft of the rotaryactuator to a plurality of ball bearings.

According to the invention, the shaft of the rotary actuator issupported by at least one bearing set comprised of a plurality of ballbearings having respective outer rings which are laminated through anin-between spacing and respective inner rings which are laminatedthrough the medium of an in-between elastic member. Each ball bearing,though being an inexpensive ball bearing of non-special specification,has its inner and outer rings which are uniformly urged against all ofthe balls so that the bearing set exhibit high rigidity in the radialdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged sectional view showing a bearing structure, whichstands for an essential part of a magnetic disc device, according to anembodiment of the invention.

FIG. 2 is a longitudinal sectional view showing an embodiment of amagnetic disc device of the invention.

FIG. 3 is a sectional view showing a bearing structure for use with therotational shaft of a rotary actuator according to another embodiment ofthe invention.

FIGS. 4 to 6 are fregmentary sectional views showing bearing structuresaccording to further embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a bearing structure used for the rotational shaft of arotary actuator illustrated in FIG. 2.

As shown in FIG. 2, a magnetic disc device 1 incorporating this bearingstructure comprises a spindle 4 directly coupled to a motor 2 andsupporting a plurality of magnetic discs 3 for rotation, a rotaryactuator 10 which has a rotational shaft 7 for supporting head arms 6respectively having magnetic heads 5 at their tip ends and which isdriven by a voice coil motor comprised of magnets 8 and a coil 9 torotate the magnetic heads 5, a base 11 for supporting these components,and a cover 12 for enclosure of the above components. When the rotaryactuator 10 is driven, the head arms 6 are rotated together with therotational shaft 7 so that the magnetic heads 5 can be positioned atdesired tracks on the magnetic discs 3 which are driven by the motor 2to rotate on. This positioning operation is performed through servocontrol.

The bearing structure for the shaft 7 is best seen in FIG. 1.

The shaft 7 has an upper end supported by a bearing set 13 and a lowerend supported by a bearing set 14. Each of the bearing sets 13 and 14has substantially the same construction and is subjected to bonding forassemblage under a spring bias as will be described later.

The upper bearing set 13 has two laminated ball bearings 15 and 16.These ball bearings 15 and 16 are not of high accuracy pursuant to aspecial specification but they are ordinary ones. Outer rings 15a and16a of the respective ball bearings 15 and 16 are bonded to acylindrical housing 17 and their inner rings 15b and 16b are bonded to asleeve 18 which is axially slidably fitted on the shaft 7. The outerrings 15a and 16a clamp or sandwich an in-between annular spacer 19having a thickness of t₁ and the inner rings 15b and 16b clamp orsandwich an in-between waved or sinuous washer 20. The waved or sinuouswasher 20 is a resilient ring washer having three or more peaks. Thus,the waved or sinuous washer 20 forms an elastic member of asubstantially circular configuration having a plane in which a pluralityof alternate peaks and valleys perpendicularly intersect. Sandwichedbetween the inner ring 15b and a flange 18a of the sleeve 18 is a rubberring 21. The sleeve 18 is secured to the shaft 7 by means of a screw 22and a washer 23.

The lower bearing set 14 has two laminated ball bearings 24 and 25 whichare of the standard specification. Outer rings 24a and 25a of therespective ball bearings 24 and 25 are bonded to a cylindrical housing26 and their inner rings 24b and 25b are bonded to a sleeve 27 which isslidably fitted on the shaft 7. A spacer 28 is sandwiched between theouter rings 24a and 25a, a waved washer 29 is sandwiched between theinner rings 24b and 25b, and a rubber ring 30 is sandwiched between theinner ring 25b and a flange 27a of the sleeve 27. The rubber ring 30 maybe replaced by other elastic member.

A thrust spring 31 is applied about a lower end portion of the shaft 7by means of an end plate 32 and a screw 33. This spring 31 exerts on theshaft 7 a force F which urges it downwards and on the sleeve 27 anopposite force F which urges it upwards.

The bearing set 13 is assembled in a manner as described below.

For assemblage, dimensions of the ball bearings 15 and 16, housing 17and sleeve 18 are so set as to enable the outer rings 15a and 16a toloosely fit in the housing with clearance and also to enable the innerrings 15b and 16b to loosely fit on the sleeve 18 with clearance. Thus,the fitting of the outer rings 15a and 16a in the housing 17 has a playand these outer rings are appreciably movable along the housing 17.Similarly, the fitting of the inner rings 15b and 16b on the sleeve 18has a play and these inner rings are appreciably movable along thesleeve 18. The outer circumferential surfaces of the outer rings 15a and16a are coated with a thermosetting adhesive and the innercircumferential surfaces of the inner rings 15b and 16b are coated withthe same adhesive. Then, the ball bearings 15 and 16 having their outerand inner rings coated with the adhesive, the spacer 19, the wavedwasher 20 and the rubber ring 21 are put together, thus completingtemporary assemblage.

In the temporary assembly, the force F urging the shaft 7 downwards isexerted on the inner ring 15b of the ball bearing 15 through the flange18a and rubber ring 21. This force F exerting on the inner ring 15b istransmitted to the outer ring 15a through a ball 15c to urge the outerring 15a downwards. Consequently, the spacer 19 and the outer ring 16aof the ball bearing 16 are urged downwards and the bottom surface of theouter ring 16a is urged by the force F against a reference surface 17aof the housing 17 to make intimate contact therewith. Thus, the postureof the outer ring 16a is controlled by the reference surface 17a. Withthe spacer 19 being in close contact with the outer ring 16a, the outerring 15a makes intimate contact with the upper surface of the spacer 19for its posture control. Since the outer rings 15a and 16a are inintimate contact with each other with the spacer 19 sandwichedtherebetween, the waved washer 20 sandwiched between the inner rings 15band 16b is deformed elastically to urge the inner ring 15b upwards andthe inner ring 16 b downwards. Geometrical dimensions of the wavedwasher 20 are determined such that when the waved washer 20 iscompressed to a thickness equal to the thickness t₁ of the spacer 19, aforce of 1/2 F is generated by the waved washer 20. The 1/2 F forcegenerated by the waved washer 20 is representative of upward anddownward component forces exerting on the inner rings 15b and 16b,respectively.

The upper inner ring 15b therefore opposes the downward force F and isurged upwards by a force F-F/2(=F/2) while the lower inner ring 16b isurged downwards by the F/2 force.

The upper inner ring 15b deforms the rubber ring 21 accordingly andtakes the posture of uniformly urging against all of the balls 15c.Consequently, the upper inner ring 15b is held in position by the outerring 15a through the medium of all of the balls 15c. Similarly, thelower inner ring 16b deforms the waved washer 20 accordingly and takesthe posture of uniformly urging against all of balls 16c so as to beheld in position by the outer ring 16a through the medium of all of theballs 16c.

In this way, the upper ball bearing 15 has the outer and inner rings 15aand 15b which uniformly urge against all of the plural balls 15carranged side by side throughout the circumference of these rings andthe lower ball bearing 16 also has the outer and inner rings 16a and 16bwhich uniformly urge against all of the plural balls 16c arranged sideby side throughout the circumference of these rings.

Under the temporary assembly condition, the adhesive is heated forsetting to the end that the outer rings 15a and 16a are bonded to thehousing 17 and the inner rings 15b and 16b are bonded to the sleeve 18,thereby completing the bearing set 13.

In the thus assembled bearing set 13, the ball bearing 15 has the outerand inner rings 15a and 15b which are in uniform contact with all of theplural balls 15c arranged side by side throughout the circumference ofthese rings and the ball bearing 16 likewise has the outer and innerrings 16a and 16b which are in uniform contact with all of the pluralballs 16c arranged side by side throughout the circumference of theserings, thus making it possible to heighten the radial rigidity of thebearing set 13. In effect, thanks to the laminated ball bearings 15 and16, the radial rigidity of the bearing set 13 is comparable to that of abearing set typically applicable to machine tools which is fabricated byusing two ball bearings in back to back, face to face or parallelcombination pursuant to a special specification, and the shaft 7 can besupported rigidly by the bearing set 13.

Due to the fact that the inner and outer rings of each of the ballbearings 15 and 16 are bonded for fixing while being loaded with theequal force (F/2) for urging against the balls, the ball bearings 15 and16 can equally share a load applied on the shaft, thus having an equallife. Accordingly, the bearing set 13 can have a maximized life.

As will be seen from the foregoing description, the spacer 19, wavedwasher 20 and rubber ring 21 are indispensable members for assemblagebut they do not play a particular role after bonding.

The lower bearing set 14 can be assembled in the same manner as thatdescribed previously, so that the outer and inner rings 24a and 24b ofthe ball bearing 24 are bonded to the housing 26 and the sleeve 7 whilebeing in uniform contact with all balls 24c and the outer and innerrings 25a and 25b of the ball bearing 25 are bonded to the housing 26and sleeve 27 while being in uniform contact with all balls 25c, therebyheightening the radial rigidity of the bearing set 14.

The rotational shaft 7 can be supported rigidly at its upper and lowerend portions by the bearing sets 13 and 14 to enable the rotary part ofthe rotary actuator 10 to have a high mechanical resonance frequencywhich is not liable to induce vibrations in the servo control andtherefore the magnetic head 5 can be held in position with highaccuracy. In addition, the shaft 7 can be simplified in shape thanks tothe use of the ball bearings, and the bearing structure can beinexpensive because the additional provision of thrust bearings is notneeded and the ball bearing of the standard specification suffices.

As particularly shown in FIG. 2, a spring 34 operating in the radialdirection and a pusher 35 are built in a lower portion of the shaft 7.Under the application of a spring force of the spring 34, the pusher 35urges the sleeve 27 in the radial direction to radially offset the same.This eliminate the adverse influence of a play between the shaft 7 andthe sleeve 27.

FIG. 3 illustrates a modified embodiment of the invention. In FIG. 3,members like those shown in FIG. 1 are denoted by like referencecharacters and will not be described. In this modification, the shaft 7is supported at its upper end by the same bearing set 13 as that of FIG.1 and at its lower end by a single ball bearing 350. The deviceconstruction shown in FIG. 2 clearly indicates that the bearingstructure is carried on the base 11 of large weight and so the amplitudeof unwanted vibration at the lower end portion is smaller than theamplitude of vibration at the upper end portion. Therefore, only theupper bearing set 13 may preferably be incorporated with the componentforce distributing configuration based on the waved washer 20 to reducethe cost effectively.

The essential part of another embodiment of bearing structure accordingto the invention is illustrated in FIG. 4 in which components like thoseof FIG. 1 are designated by like reference characters for avoidance ofprolixity of explanation. A bearing set 40 has inner rings 15b and 16bwhich are postured to profile the shaft 7 and outer rings 15a and 16awhich follow the inner rings 15b and 16b. For assemblage, the innerrings 15b and 16b are loosely fitted on the sleeve 18, with a spacer 41corresponding to the spacer 19 of FIG. 1 sandwiched between these innerrings, and the outer rings 15a and 16a clamp an in-between waved washer42 corresponding to the waved washer 20 of FIG. 1, with a waved washer43 corresponding to the rubber ring 21 of FIG. 1 interposed between theouter ring 16a and the reference surface 17a of the housing 17. In thisembodiment, the flange 18a of the sleeve 18 serves as a referencesurface.

The force F urging the shaft 7 downwards urges the inner ring 15b,spacer 41 and inner ring 16b downwards so that the outer ring 16a isurged downwards through the medium of the balls 16c. The inner ring 15burges against the flange 18a to take the controlled posture, the innerring 16b is forced through the spacer 41 to take the controlled posture,and the outer ring 16a is forced through the balls 16c to take thecontrolled posture such that the outer ring 16a comes in uniform contactwith all of the balls 16c. The outer ring 15a is urged upwards by thespring force (F/2) of the waved washer 42 so as to be forced through theballs 15c to take the controlled posture such that the outer ring 15acomes in uniform contact with all of the balls 15c. The inner rings 15band 16b are bonded to the sleeve 18 while taking the controlled postureas above, and the outer rings 15a and 16 a are bonded to the housing 17while taking the controlled posture as above.

Thus, as in the precedence, the inner and outer rings of each of theball bearings 15 and 16 are in uniform contact with all of the balls 15cor all of the balls 16c to heighten the radial rigidity of the bearingset 40. Consequently, the bearing set 40 can exhibit rigidity comparableto that of the bearing set 13.

In the foregoing embodiments, each of the bearing sets 13, 14 and 40 hastwo laminated ball bearings but three or more ball bearings may belaminated as necessary and the rigidity can be more heightened as thenumber of the ball bearings increases.

Referring to FIG. 5, there is illustrated still another embodiment ofbearing structure wherein one of the ball bearings of a bearing set hasan outer ring which is prolonged in the axial direction. This embodimentof FIG. 5 is advantageous in that the spacer 19 interposed between theouter rings 15a and 16a of the bearing set 13 shown in FIG. 3 and thespacer 41 interposed between the inner rings 15b and 16b shown in FIG. 4can be dispensed with. Specifically, a bearing set 50 of the FIG. 5embodiment includes a ball bearing 15 having an outer ring 15a' whoseaxial thickness or height is made larger than that of the inner ring 15band of outer and inner rings 16a and 16b of a lower ball bearing 16,measuring a dimension that permits the outer ring 15a' to suppress thewaved washer 20 until a repulsive force of waved washer 20 which opposesthe force F applied by the thrust spring 31 to the bearing set throughthe shaft 7 grows to generate the predetermined force F and the distance19' disappears.

FIG. 6 illustrates a further embodiment of bearing set wherein anelastic member 43' is provided at the bottom of a set of axiallyarranged outer rings which clamp an in-between waved washer 42, wherebya load applied on the outer ring set can be transmitted to the referencesurface 17a formed interiorly of the housing 17. As the elastic member43', an ordinary rubber member may be used which can withstand the axialforce F applied by the thrust spring 31. In this embodiment, the wavedwasher 43 of the FIG. 4 embodiment can be eliminated.

It will be appreciated that, in the foregoing embodiments, the upperball bearing comprised of components 15a, 15b and 15c and the lower ballbearing comprised of components 16a, 16b and 16c are axially slidden,under the application of the repulsive force F of the waved washer 20 or42, to positions where each of the ball bearings equally shares thecomponent force F/2 generated by the waved washer and then each ballbearing is bonded to the housing at that position. In an example ofbonding, a double-fluid admixed epoxy bonding agent is heated at 80° C.for a predetermined time and it is simply necessary for the waved washer20, 42 or 43, spacer 19 or 41 and elastic member 43' to withstand theabove heating condition. The thus assembled bearing set having the ballbearings bonded to the housing 17 at positions where they equally sharethe component force F/2 can fulfill its rigidity enhancing function fora long time.

Although the invention has been described by way of the magnetic discdevice for the illustrative purpose, the present invention is notlimited thereto but may be applied efficiently to construct a bearingset which is used for heightening the radial rigidity and suppressingunwanted vibrations in a rotary body such as an optical disc or anopto-magnetic disc.

We claim:
 1. A rotary actuator comprising:a rotational shaft; aplurality of bearing sets arranged in spaced relationship along alongitudinal axis of said rotational shaft to support opposite ends ofsaid rational shaft, each of said plurality of bearing sets including anouter ring and an inner ring which are concentric with respect to saidrotational shaft, and a plurality of ball bearings interposed betweensaid outer and inner rings; an elastic member interposed between therespective inner rings of said plurality of bearing sets and havingapplied thereto a force in an axial direction of said rotational shaft,said elastic member being a substantially circular sinuous washer havinga plane in which a plurality of alternate peaks and valleysperpendicularly intersect; and wherein said plurality of balls bearingsare situated interiorly of a housing of said bearing set in the axialdirection of said rotational shaft such that, under the application ofan axial force, the ball bearings share substantially equally componentforces generated by said elastic member.
 2. A rotary actuator accordingto claim 1, wherein said elastic member is a substantially circularsinuous washer having a plane in which a plurality of alternate peaksand valleys perpendicularly intersect.
 3. A rotary actuator having ahead for recording and reproducing information in a disk device, therotary actuator comprising:a rotational shaft; a plurality of bearingsets arranged in spaced relationship along the axis of said rotationalshaft to support opposite ends of said rotational shaft, each of saidplurality of bearing sets including an outer ring and an inner ringconcentric with said rotational shaft, and a plurality of ball bearingsinterposed between said outer and inner rings and situated in interiorlyof a housing; an elastic member interposed between the respective innerrings of said plurality of bearing sets and having applied thereto aforce in the axial direction of said rotational shaft to intervene inone of the sets of outer rings boded to said housing or of the innerrings bonded to said rotational shaft, and a spacer member of apredetermined thickness intervening in the other set which opposes saidone set, said predetermined thickness being of a geometrical dimensionto define a gap between said spacer member and the other set, whereinsaid gap disappears when the axial force exerted on said elastic memberreaches a predetermined value.
 4. A rotary actuator according to claim3, wherein said elastic member is a substantially circular sinuouswasher having a plane in which a plurality of alternate peaks andvalleys perpendicularly intersect.
 5. A rotary actuator comprising:astationary housing; a rotational shaft; a plurality of bearing setsarranged in spaced relationship along the axis of said rotational shaftto support said rotational shaft at opposite ends thereof within saidhousing, each of said plurality of bearing sets including an outer ringand an inner ring which are concentric with said rotational shaft, and aplurality of ball bearings interposed between said outer and innerrings; a sleeve slidably mounted between said rotational shaft and saidinner ring of said ball bearing sets; an elastic member interposedbetween the respective inner rings of said plurality of bearing sets forapplying thereto a force in the axial direction of said rotationalshaft; wherein said plurality of ball bearing sets are arrayed in theaxial direction of said rotational shaft such that, under theapplication of an axial force, said plurality of ball bearingssubstantially equally share component forces generated by said elasticmember; and wherein said inner ring of the respective ball bearing setsis bonded to said sleeve while said outer ring of the respective ballbearing sets is bonded to said housing in a state in which said axialforce is applied.
 6. A rotary actuator according to claim 5, whereinsaid elastic member intervenes in one of the sets of the outer rings andof the inner rings, a spacer member of a predetermined thicknessintervenes in the other set which opposes said one set, saidpredetermined thickness being of a geometrical dimension permitting agap between said spacer member and the other set to be zero when theaxial force exerted on said elastic member through said one set reachesa predetermined value, and wherein said inner rings are bonded to saidrotational shaft and said outer rings are bonded to said housing whilesaid gap is zero.
 7. A rotary actuator according to claim 5, whereinsaid elastic member is a substantially circular sinuous washer having aplane in which a plurality of alternate peaks and valleysperpendicularly intersect.
 8. A rotary actuator comprising:a pluralityof bearing sets arranged in spaced relationship along the axis of saidrotational shaft to support opposite ends of said rotational shaft, eachof said plurality of bearing sets including an outer ring and an innerring which are concentric with said rotational shaft, and a plurality ofball bearings interposed between said outer and inner rings; an elasticmember interposed between the respective inner rings of said pluralityof bearing sets and having applied thereto a force in the axialdirection of said rotational shaft; said elastic member intervenes inone of the sets of the outer rings and of the inner rings, a spacermember of a predetermined thickness intervenes in the other set whichopposes said one set, said predetermined thickness being of geometricaldimension permitting a gap between said spacer member and the other setto be zero when the axial force exerted on said elastic member throughsaid one set reaches a predetermined value; said plurality of ballbearings are situated interiorly of a housing of said bearing sets inthe axial direction of said rotational shaft such that, under theapplication of an axial force, the ball bearings share substantiallyequally component forces generated by said elastic member; and whereinsaid inner rings are bonded to said rotational shaft and said outerrings are bonded to said housing while said gap is zero.